Combined heat and power system

ABSTRACT

A CHP system includes a combustor (heat source), a Rankine cycle apparatus, and a second heat exchanger. The Rankine cycle apparatus includes, as an evaporator, a first heat exchanger that absorbs thermal energy produced in the combustor. The second heat exchanger is located closer to the combustor than is the evaporator, absorbs thermal energy produced in the combustor, and transfers the thermal energy to a heat medium.

This is a continuation of International Application No.PCT/JP2014/002107, with an international filing date of Apr. 14, 2014,which claims the foreign priority of Japanese Patent Application No.2013-089215, filed on Apr. 22, 2013, the entire contents of both ofwhich are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to combined heat and power systems.

2. Description of Related Art

A combined heat and power system (CHP system) is a system configured tocreate several forms of energy such as heat and electricitysimultaneously from a single or plurality of sources. In recent years,not only large-scale CHP systems but also CHP systems installable inrelatively small-scale facilities such as hospitals, schools, andlibraries and CHP systems for use in ordinary houses (so-called microCHPs) have been receiving attention.

EP 2014880 A1 describes a CHP system configured to create electricityusing combustion gas produced in a gas boiler or a pellet boiler asthermal energy for a Rankine cycle apparatus. In the CHP system of EP2014880 A1, an evaporator of the Rankine cycle apparatus is locatedcloser to a heat source than is a heat exchanger for producing hotwater; that is, the evaporator is located on the upstream side of a flowpath of the combustion gas. With this configuration, thermal input tothe evaporator is increased, and the rotary power of an expander of theRankine cycle apparatus is increased, in consequence of which increasedelectricity is obtained.

SUMMARY OF THE INVENTION

Conventional CHP systems have a problem in that when the operation ofthe Rankine cycle apparatus ceases due to defects, including failure ofdevices such as the expander and the pump and leakage of the workingfluid, the entire system is forced to stop operation.

One non-limiting and exemplary embodiment provides a CHP system capableof supplying thermal energy even when the operation of its Rankine cycleapparatus is stopped.

Additional benefits and advantages of the disclosed embodiments will beapparent from the specification and Figures. The benefits and/oradvantages may be individually provided by the various embodiments andfeatures of the specification and drawings disclosure, and need not allbe provided in order to obtain one or more of the same.

In one general aspect, the techniques disclosed here feature a combinedheat and power system including: a heat source; a Rankine cycleapparatus including, as an evaporator for heating a working fluid, afirst heat exchanger that absorbs thermal energy produced in the heatsource; and a second heat exchanger that is a heat exchanger for heatinga heat medium different from the working fluid of the Rankine cycleapparatus, that is located closer to the heat source than is the firstheat exchanger, and that absorbs thermal energy produced in the heatsource and transfers the thermal energy to the heat medium.

The above CHP system can supply thermal energy even when the operationof the Rankine cycle apparatus is stopped.

These general and specific aspects may be implemented using a system, amethod, a computer program, and any combination of systems, methods, andcomputer programs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram of a combined heat and power systemaccording to an embodiment of the present disclosure.

FIG. 2 is a perspective view of a heat exchange unit.

FIG. 3 is a configuration diagram of a combined heat and power systemaccording to a first modification.

FIG. 4 is a configuration diagram of a combined heat and power systemaccording to a second modification.

FIG. 5A is a configuration diagram of a combined heat and power systemaccording to a third modification.

FIG. 5B is a schematic cross-sectional view showing the positionalrelationship among a combustor, a first heat exchanger (evaporator), anda second heat exchanger in the combined heat and power system shown inFIG. 5A.

FIG. 5C is a schematic cross-sectional view showing the positionalrelationship among a combustor, a first heat exchanger (evaporator), asecond heat exchanger, and a third heat exchanger of the secondmodification when the third heat exchanger is added to the combined heatand power system shown in FIG. 5A.

FIG. 6 is a configuration diagram of a combined heat and power systemaccording to a fourth modification.

FIG. 7 is a configuration diagram of a combined heat and power systemaccording to a fifth modification.

FIG. 8A is a perspective view of a heat exchange unit according to amodification.

FIG. 8B is a schematic cross-sectional view of the heat exchange unitshown in FIG. 8A.

FIG. 8C is a perspective view of a heat exchange unit according toanother modification.

DETAILED DESCRIPTION

The CHP system described in EP 2014880 A1 is seemingly capable ofproducing hot water even when the operation of the Rankine cycleapparatus is stopped. However, continuously combusting the fuel in theboiler may cause defects such as thermal damage to the evaporator of theRankine cycle apparatus, thermal decomposition of the working fluid, andthermal decomposition of the lubricating oil. In the case of theconventional CHP system, therefore, the entire system needs to beshutdown when the operation of the Rankine cycle apparatus is stopped.

A first aspect of the present disclosure provides a combined heat andpower system including: a heat source; a Rankine cycle apparatusincluding, as an evaporator for heating a working fluid, a first heatexchanger that absorbs thermal energy produced in the heat source; and asecond heat exchanger that is a heat exchanger for heating a heat mediumdifferent from the working fluid of the Rankine cycle apparatus, that islocated closer to the heat source than is the first heat exchanger, andthat absorbs thermal energy produced in the heat source and transfersthe thermal energy to the heat medium.

In the CHP system of the first aspect, the evaporator (first heatexchanger) of the Rankine cycle apparatus is located farther from theheat source than is the second heat exchanger, which is why thetemperature of the medium (e.g., the combustion gas) that impartsthermal energy to the evaporator can be lowered. Consequently, even whenthe operation of the Rankine cycle apparatus is stopped, it is possibleto heat the heat medium in the second heat exchanger while preventingdefects such as thermal damage to the evaporator and thermaldecomposition of the working fluid of the Rankine cycle apparatus.

A second aspect of the present disclosure provides the combined heat andpower system as set forth in the first aspect, wherein the second heatexchanger is in direct contact with the first heat exchanger or inindirect contact with the first heat exchanger via athermally-conductive member. With such a configuration, the heat of theevaporator (first heat exchanger) of the Rankine cycle apparatus istransferred to the second heat exchanger since the second heat exchangeris in direct contact with the evaporator or in indirect contact with theevaporator via the thermally-conductive member. Consequently, even whenthe operation of the Rankine cycle apparatus is stopped, it is possibleto efficiently heat the heat medium in the second heat exchanger whilepreventing defects such as thermal damage to the evaporator and thermaldecomposition of the working fluid of the Rankine cycle apparatus.

A third aspect of the present disclosure provides the combined heat andpower system as set forth in the first or second aspect, wherein theheat source is a combustor that produces flame and combustion gas. Withthe use of the combustor that produces flame and combustion gas as theheat source, high-temperature thermal energy can easily be obtained.This can result in an improvement in the efficiency of electricitygeneration by the Rankine cycle apparatus. Furthermore, the sizes of thefirst heat exchanger and the second heat exchanger can be reduced.

A fourth aspect of the present disclosure provides the combined heat andpower system as set forth in the third aspect, wherein the first heatexchanger and the second heat exchanger are disposed on an exhaust pathof the combustion gas so that the combustion gas passes through thesecond heat exchanger and the first heat exchanger in this order. Withsuch a configuration, the first heat exchanger and the second heatexchanger can absorb thermal energy directly from the combustion gas.Therefore, both the energy of the flame and the energy of the combustiongas are efficiently absorbed in the first heat exchanger and the secondheat exchanger, and hence high energy use efficiency can be achieved.

A fifth aspect of the present disclosure provides the combined heat andpower system as set forth in any one of the first to fourth aspects,further including: a flow path connected to the second heat exchanger soas to feed the heat medium to the second heat exchanger; and a flow rateregulator disposed in the flow path. By control of the flow rateregulator, the amount of the heat medium flowing through the second heatexchanger can be regulated. That is, it is possible not only to regulatethe amount of the heat medium to be heated on demand, but also to adjustthe ratio of the thermal output (kWt) to the electrical output (kWe) toan optimum range.

A sixth aspect of the present disclosure provides the combined heat andpower system as set forth in the fifth aspect, wherein the Rankine cycleapparatus includes a detector that detects an amount of generatedelectricity, and the combined heat and power system further includes acontroller that controls the flow rate regulator based on the amount ofgenerated electricity detected by the detector. With such aconfiguration, the electrical output and the thermal output can befreely and finely adjusted on demand.

A seventh aspect of the present disclosure provides the combined heatand power system as set forth in any one of the first to sixth aspects,wherein the combined heat and power system is capable of heating theheat medium by feeding the heat medium to the second heat exchanger whenthe Rankine cycle apparatus is not generating electricity. With such aconfiguration, it is possible to heat the heat medium in the second heatexchanger while preventing defects such as thermal damage to the firstheat exchanger and thermal decomposition of the working fluid, therebyimproving the convenience for users.

An eighth aspect of the present disclosure provides the combined heatand power system as set forth in the third or fourth aspect, wherein thecombustor includes a plurality of discrete combustors capable ofproducing the flame and the combustion gas independently of each other,and a positional relationship between the second heat exchanger and theplurality of discrete combustors is determined so that the combustiongas produced in at least one of the discrete combustors flows withoutpassing through the second heat exchanger. With such a configuration,the combustion gas can be delivered directly to the first heat exchangerand, therefore, the temperature of the combustion gas reaching the firstheat exchanger can be made high. Thus, the amount of heat imparted tothe first heat exchanger can be increased. Consequently, the amount ofelectricity generated by the Rankine cycle apparatus can be increasedand, at the same time, the efficiency of electricity generation can beimproved.

A ninth aspect of the present disclosure provides the combined heat andpower system as set forth in any one of the first to eighth aspects,further including a third heat exchanger located farther from the heatsource than is the first heat exchanger, wherein the third heatexchanger transfers thermal energy produced in the heat source to theheat medium. With the use of the third heat exchanger, that remainingportion of the thermal energy produced in the heat source which has notbeen absorbed in the first heat exchanger and the second heat exchangercan be recovered. Consequently, the efficiency of use of the thermalenergy produced in the heat source is improved.

A tenth aspect of the present disclosure provides the combined heat andpower system as set forth in the ninth aspect, wherein the third heatexchanger is connected to the second heat exchanger so that the heatmedium having passed through the third heat exchanger flows into thesecond heat exchanger. With such a configuration, water with arelatively low temperature flows through the third heat exchanger, whilewater with a relatively high temperature flows through the second heatexchanger. Hence, a larger amount of thermal energy can be absorbed inthe second heat exchanger and the third heat exchanger. Consequently,the efficiency of use of the thermal energy produced in the heat sourceis improved.

An eleventh aspect of the present disclosure provides the combined heatand power system as set forth in the second aspect, wherein thethermally-conductive member is a heat pipe that allows the first heatexchanger and the second heat exchanger to be in indirect contact witheach other. With the use of the heat pipe, heat transfer from the firstheat exchanger to the second heat exchanger can be facilitated.

Hereinafter, embodiments of the present disclosure will be describedwith reference to the drawings. It should be noted that the presentdisclosure is not limited by the embodiments described hereinafter.

As shown in FIG. 1, a combined heat and power system 100 (hereinafterreferred to as a “CHP system”) of the present embodiment includes aboiler 10, a Rankine cycle apparatus 20, a first fluid circuit 30, asecond fluid circuit 40, and a controller 50. The CHP system 100 isconfigured to create hot water and electricity simultaneously orseparately using thermal energy produced in the boiler 10. The word“simultaneously” is used to mean that electricity can be supplied whilehot water is supplied. The word “separately” is used to mean thatelectricity alone can be supplied while supply of hot water is stopped,and hot water alone can be supplied while supply of electricity isstopped.

When the Rankine cycle apparatus 20 is in operation, electricityproduced in the Rankine cycle apparatus 20, hot water produced in thefirst fluid circuit 30, and hot water produced in the second fluidcircuit 40 can be supplied to the outside. When the Rankine cycleapparatus 20 is not in operation, hot water produced in the second fluidcircuit 40 can be supplied to the outside.

In the present embodiment, the heat medium flowing in the first fluidcircuit 30 is water. However, the heat medium to be heated in the firstfluid circuit 30 is not limited to water. The first fluid circuit 30 maybe configured to heat another heat medium such as brine and air. In thepresent embodiment, the heat medium flowing in the second fluid circuit40 is also water. The heat medium to be heated in the second fluidcircuit 40 is not limited to water either. The second fluid circuit 40may be configured to heat another liquid heat medium such as brine.

The boiler 10 includes a combustion chamber 12 and a combustor 14. Anexhaust port is provided at the top of the combustion chamber 12. Thecombustor 14 is a heat source that produces flame and combustion gas,and is disposed inside the combustion chamber 12. The combustion gasproduced in the combustor 14 moves upwardly in the internal space of thecombustion chamber 12, and is discharged outside through the exhaustport. With the use of the combustor 14 that produces flame andcombustion gas as the heat source in the CHP system 100,high-temperature thermal energy can easily be obtained. Consequently,the efficiency of electricity generation by the Rankine cycle apparatus20 can be improved. Another device such as an air blower may be disposedinside the boiler 10.

The boiler 10 is, for example, a gas boiler. When the boiler 10 is a gasboiler, a fuel gas such as natural gas and biogas is supplied to thecombustor 14. The combustor 14 produces flame and high-temperaturecombustion gas by combusting the fuel gas.

The Rankine cycle apparatus 20 includes an expander 21, a condenser 22,a pump 23, and an evaporator 24. These components are connectedcircularly by a plurality of pipes in the order in which they arementioned, so that a closed circuit is formed. The Rankine cycleapparatus 20 may be provided with a commonly-known regenerator or thelike.

The expander 21 expands the working fluid heated in the boiler 10. Theexpander 21 is, for example, a positive-displacement expander or aturbo-expander. Examples of the positive-displacement expander includescroll expanders, rotary expanders, screw expanders, and reciprocatingexpanders. The turbo-expander is a so-called expansion turbine. Anelectricity generator 26 is connected to the rotating shaft of theexpander 21. The electricity generator 26 is driven by the expander 21.The Rankine cycle apparatus 20 is provided with a detector 27 thatdetects the amount of electricity (kWe) generated by the electricitygenerator 26. The detector 27 is typically a wattmeter. The informationon the amount of electricity detected by the detector 27 is transmittedto the controller 50.

The condenser 22 allows heat exchange to take place between water in thefirst fluid circuit 30 and the working fluid discharged from theexpander 21, thereby cooling the working fluid and heating the water. Acommonly-known heat exchanger, such as a plate heat exchanger, a doubletube heat exchanger, and a fin tube heat exchanger, can be used as thecondenser 22. The type of the condenser 22 is selected as appropriatedepending on the type of the heat medium in the first fluid circuit 30.When the heat medium in the first fluid circuit 30 is a liquid such aswater, a plate heat exchanger or a double tube heat exchanger can besuitably used as the condenser 22. When the heat medium in the firstfluid circuit 30 is a gas such as air, a fin tube heat exchanger can besuitably used as the condenser 22.

The pump 23 draws the working fluid flowing from the condenser 22,pressurizes the working fluid, and delivers the pressurized workingfluid to the evaporator 24. A common positive-displacement pump orturbo-pump can be used as the pump 23. Examples of thepositive-displacement pump include piston pumps, gear pumps, vane pumps,and rotary pumps. Examples of the turbo-pump include centrifugal pumps,mixed flow pumps, and axial-flow pumps.

The evaporator 24 is a first heat exchanger that absorbs thermal energyfrom the combustion gas produced in the combustor 14. Specifically, theevaporator 24 is disposed inside the boiler 10 so as to be locatedrelatively far from the combustor 14. A fin tube heat exchanger, asshown in FIG. 2, can be used as the evaporator 24. The combustion gasproduced in the combustor 14 and the working fluid of the Rankine cycleapparatus 20 exchange heat in the evaporator 24. Thus, the working fluidof the Rankine cycle apparatus 20 is heated and evaporated. Not only theheat of the combustion gas but also the radiant heat from the flame isapplied to the evaporator 24.

An organic working fluid can be suitably used as the working fluid ofthe Rankine cycle apparatus 20. Examples of the organic working fluidinclude halogenated hydrocarbons, hydrocarbons, and alcohols. Examplesof the halogenated hydrocarbons include R-123 and R-245fa. Examples ofthe hydrocarbons include alkanes such as propane, butane, pentane, andisopentane. Examples of the alcohols include ethanol. These organicworking fluids may be used alone, or a mixture of two or more thereofmay be used. Also, there may be some cases where an inorganic workingfluid such as water, carbon dioxide, and ammonia can be used as theworking fluid.

The first fluid circuit 30 is connected to the condenser 22 of theRankine cycle apparatus 20 so as to feed water to the condenser 22. Thewater in the first fluid circuit 30 is heated by the working fluiddischarged from the expander 21.

When the heat medium to be heated through the first fluid circuit 30 isa liquid such as water, the first fluid circuit 30 can be formed by oneor more pipes. When the heat medium to be heated through the first fluidcircuit 30 is a gas such as air, the first fluid circuit 30 can beformed by an air path or a duct for the flow of the gas.

The second fluid circuit 40 has a second heat exchanger 42, a flow path44 a, a flow path 44 b, and a flow rate regulator 46. The second heatexchanger 42 is disposed inside the boiler 10 so as to be located closerto the combustor 14 than is the evaporator 24 of the Rankine cycleapparatus 20 and to be in contact with the evaporator 24. The secondheat exchanger 42 absorbs thermal energy from the combustion gasproduced in the combustor 14 and transfers the thermal energy to water(heat medium). That is, the combustion gas produced in the combustor 14and water in the second fluid circuit 40 exchange heat in the secondheat exchanger 42. Thus, the water in the second fluid circuit 40 isheated. The radiant heat from the flame produced in the combustor 14 isalso applied to the second heat exchanger 42. The second heat exchanger42 may be heated directly by the flame produced in the combustor 14 insome cases.

The first fluid circuit 30 and the second fluid circuit 40 are each acircuit provided independently of the working fluid circuit of theRankine cycle apparatus 20. This means that the fluid flowing in thefirst fluid circuit 30 and the working fluid of the Rankine cycleapparatus 20 are never mixed together, and that the fluid flowing in thesecond fluid circuit 40 and the working fluid of the Rankine cycleapparatus 20 are never mixed together. The second heat exchanger 42 is aheat exchanger for heating a heat medium (water in the presentembodiment) different from the working fluid of the Rankine cycleapparatus 20.

A fin tube heat exchanger, as shown in FIG. 2, can be used as the secondheat exchanger 42. The flow paths 44 a and 44 b are connected to thesecond heat exchanger 42 so as to feed water to the second heatexchanger 42. The flow paths 44 a and 44 b can each be formed by one ormore pipes. The flow rate regulator 46 is disposed in the flow path 44a. The flow rate regulator 46 is typically a flow rate regulating valve.By controlling the flow rate regulator 46, the amount of water flowingthrough the second heat exchanger 42 can be regulated. That is, it ispossible not only to regulate the amount of hot water to be produced onthe demand for hot water (heat) but also to adjust the ratio(heat-to-power ratio) of the thermal output (kWt) to the electricaloutput (kWe) to an optimum range.

The heat-to-power ratio can be adjusted also by designing the evaporator24 and the second heat exchanger 42 appropriately. For example, theevaporator 24 may have relatively high capacity, while the second heatexchanger 42 may have relatively low capacity. Specifically, in theexample shown in FIG. 2, the dimension of the evaporator 24 in theheight direction (the flow direction of the combustion gas) can be setlarge, and the dimension of the second heat exchanger 42 in the heightdirection can be set small. More specifically, the number of rows ofheat transfer tubes 62 a of the evaporator 24 in the height directioncan be set relatively large, and the number of rows of heat transfertubes 62 b of the second heat exchanger 42 in the height direction canbe set relatively small. With such a configuration, the Rankine cycleapparatus 20 can be endowed with sufficient capacity to generateelectricity.

Conversely, the evaporator 24 may have relatively low capacity, whilethe second heat exchanger 42 may have relatively high capacity.Specifically, in the example shown in FIG. 2, the dimension of theevaporator 24 in the height direction can be set small, and thedimension of the second heat exchanger 42 in the height direction can beset large. More specifically, the number of rows of the heat transfertubes 62 a of the evaporator 24 in the height direction can be setrelatively small, and the number of rows of the heat transfer tubes 62 bof the second heat exchanger 42 in the height direction can be setrelatively large. With such a configuration, the second heat exchanger42 can be endowed with sufficient capacity to supply hot water.

The controller 50 controls various targets such as the pump 23 of theRankine cycle apparatus 20, the combustor 14 of the boiler 10, and theflow rate regulator 46 of the second fluid circuit 40. A DSP (DigitalSignal Processor) including an A/D conversion circuit, an input/outputcircuit, a computing circuit, a memory device, etc., can be used as thecontroller 50. In the controller 50, there is stored a program foroperating the CHP system 100 properly.

The hot water produced in the first fluid circuit 30 can be supplied toequipment such as faucets, hot water heater circuits, and hot waterstorage tanks. The first fluid circuit 30 may be used to heat lukewarmwater or may be used to heat city water. The same applies to the secondfluid circuit 40.

In the present embodiment, the second heat exchanger 42 of the secondfluid circuit 40 is located closer to the combustor 14 than is theevaporator 24 of the Rankine cycle apparatus 20. Therefore, the secondheat exchanger 42 is exposed to an atmosphere of relatively hightemperature, and can absorb a large amount of thermal energy. Hence, thesecond fluid circuit 40 has high capacity to supply hot water.Additionally, that remaining portion of the thermal energy produced inthe combustor 14 which has not been absorbed in the second heatexchanger 42 is absorbed in the evaporator 24. Specifically, thecombustion gas reaching the evaporator 24 is one that has been cooled bythe second heat exchanger 42, and has a relatively low temperature. Thatis, according to the present embodiment, the temperature of thecombustion gas flowing into the evaporator 24 can be lowered by feedingwater to the second heat exchanger 42 even when the Rankine cycleapparatus 20 is not in operation. Consequently, it is possible toprevent defects such as thermal damage to the evaporator 24, thermaldecomposition of the working fluid, thermal decomposition of thelubricating oil, and excessive increase in the internal pressure of theRankine cycle apparatus 20 due to thermal expansion of the workingfluid. At the same time, hot water can be produced by use of the secondfluid circuit 40. In other words, the same operation as that of a commonhot-water boiler can be carried out in the CHP system 100 even when theRankine cycle apparatus 20 is not in operation.

The evaporator 24 of the Rankine cycle apparatus 20 and the second heatexchanger 42 of the second fluid circuit 40 are in contact with eachother in the boiler 10. Therefore, the thermal energy produced in thecombustor 14 can be imparted to the water in the second heat exchanger42 via the evaporator 24. Hence, even if the evaporator 24 absorbs thethermal energy when the Rankine cycle apparatus 20 is not in operation(when the pump 23 is not in operation), the heat can be transferred fromthe evaporator 24 to the water in the second heat exchanger 42.Consequently, it is possible to reliably prevent defects such as thermaldamage to the evaporator 24, thermal decomposition of the working fluid,thermal decomposition of the lubricating oil, and excessive increase inthe internal pressure of the Rankine cycle apparatus 20 due to thermalexpansion of the working fluid. Furthermore, an improvement in theefficiency of recovery of the thermal energy can be expected.

As shown in FIG. 2, the evaporator 24 and the second heat exchanger 42are in direct contact with each other so that heat of the evaporator 24can be directly transferred to the second heat exchanger 42 via a mediumother than air. Specifically, the evaporator 24 and the second heatexchanger 42 are each a fin tube heat exchanger, and the evaporator 24and the second heat exchanger 42 share a plurality of fins 61. Theevaporator 24 is formed of the upper halves of the fins 61 and the heattransfer tube 62 a. The second heat exchanger 42 is formed of the lowerhalves of the fins 61 and the heat transfer tube 62 b. The heat transfertube 62 a of the evaporator 24 does not communicate with the heattransfer tube 62 b of the second heat exchanger 42. The working fluidflows through the heat transfer tube 62 a, and water flows through theheat transfer tube 62 b. The heat of the evaporator 24 can beefficiently transferred via the fins 61 to the water flowing in thesecond heat exchanger 42. Thus, defects such as thermal damage to theevaporator 24, thermal decomposition of the working fluid, and thermaldecomposition of the lubricating oil, can be prevented.

In the present embodiment, the evaporator 24 and the second heatexchanger 42 form a single heat exchange unit 60. The heat exchange unit60 is disposed inside the boiler 10 so as to be located directly abovethe combustor 14. The fins 61 are aligned in the horizontal direction.The heat transfer tubes 62 a and 62 b each pierce through the fins 61 inthe horizontal direction. The spaces formed between the adjacent fins 61form an exhaust path of the combustion gas G. In other words, the secondheat exchanger 42 and the evaporator 24 are disposed on the exhaust pathof the combustion gas G so that the combustion gas G passes through thesecond heat exchanger 42 and the evaporator 24 in this order. With sucha configuration, the second heat exchanger 42 and the evaporator 24 canabsorb thermal energy directly from the combustion gas G and, therefore,high energy use efficiency can be achieved.

The structures of the evaporator 24 and the second heat exchanger 42 arenot particularly limited, as long as good heat transfer from theevaporator 24 to the second heat exchanger 42 can be achieved. Forexample, the evaporator 24 and the second heat exchanger 42 may each beformed by a serpentine heat transfer tube. In this case, the heattransfer tubes are in direct contact with each other. That is, it isdesirable that a component of the evaporator 24 be in direct contactwith a component of the second heat exchanger 42.

In the present embodiment, the second heat exchanger 42 is locatedrelatively close to the combustor 14, while the evaporator 24 is locatedrelatively far from the combustor 14. With this positional relationship,thermal input to the second heat exchanger 42 is increased, whichenables an increase in the capacity of the second fluid circuit 40 tosupply hot water.

In the present embodiment, even when water is not fed to the secondfluid circuit 40, heat can be transferred from the second heat exchanger42 to the evaporator 24 via the fins 61. Therefore, the amount of heatinput to the evaporator 24 can be increased. Additionally, when water isnot fed to the second fluid circuit 40, the combustion gas G of highertemperature can be supplied to the evaporator 24. Consequently, anincrease in the amount of electricity generated by the Rankine cycleapparatus 20 and an improvement in the efficiency of electricitygeneration can be expected.

Next, two typical operation modes of the CHP system 100 will bedescribed. The first operation mode is an operation mode used when theRankine cycle apparatus 20 is in operation. The second operation mode isan operation mode used when the Rankine cycle apparatus 20 is not inoperation.

<First Operation Mode>

In the first operation mode, the CHP system 100 can supply both hotwater and electricity to the outside. First, the pump 23 is driven tostart the operation of the Rankine cycle apparatus 20, and feed of waterto the first fluid circuit 30 is started at an appropriate time.Thereafter, supply of a fuel to the combustor 14 is started at anappropriate time, and the fuel is ignited. The working fluid of theRankine cycle apparatus 20 receives heat from combustion gas in theevaporator 24, and changes to a superheated gaseous form. Thehigh-temperature gaseous working fluid is delivered to the expander 21.In the expander 21, the pressure energy of the working fluid isconverted to mechanical energy, so that the electricity generator 26 isdriven. Thus, electricity is generated in the electricity generator 26.The working fluid discharged from the expander 21 flows into thecondenser 22. The working fluid may maintain the superheated state atthe outlet of the expander 21. In the condenser 22, the working fluid iscooled and condensed by water flowing in the first fluid circuit 30. Thewater in the first fluid circuit 30 is heated by the working fluid. Hotwater is produced in the first fluid circuit 30, and the produced hotwater is supplied to the outside. The condensed working fluid ispressurized by the pump 23, and is delivered to the evaporator 24 again.

Independently of the operation of the Rankine cycle apparatus 20, feedof water to the second fluid circuit 40 is started at an appropriatetime. The water flowing in the second fluid circuit 40 is heated by thecombustion gas. Hot water is produced also in the second fluid circuit40, and the produced hot water is supplied to the outside.

In the first operation mode, the controller 50 controls the pump 23and/or the flow rate regulator 46 based on the amount of generatedelectricity detected by the detector 27. Such control makes it possibleto freely and finely adjust the electrical output and the thermal outputon demand. For example, if a command to increase the electrical outputis input to the controller 50 (that is, when the electrical outputshould be increased), the controller 50 controls the pump 23 so as toincrease the circulation rate of the working fluid, and controls theflow rate regulator 46 so as to reduce the flow rate of water in thesecond fluid circuit 40. Specifically, the controller 50 increases therotation speed of the pump 23, and reduces the degree of opening of theflow rate regulator 46. Conversely, if a command to reduce theelectrical output is input to the controller 50 (that is, when theelectrical output should be reduced), the controller 50 controls thepump 23 so as to reduce the circulation rate of the working fluid, andcontrols the flow rate regulator 46 so as to increase the flow rate ofwater in the second fluid circuit 40. Specifically, the controller 50reduces the rotation speed of the pump 23, and increases the degree ofopening of the flow rate regulator 46. Both the control of the pump 23and the control of the flow rate regulator 46 may be carried out, or oneof the controls may be carried out alone, depending on the amount ofgenerated electricity detected by the detector 27.

Furthermore, when the controller 50 detects malfunction of the Rankinecycle apparatus 20, the controller 50 controls the flow rate regulator46 so as to increase the flow rate of water in the second fluid circuit40. For example, when the controller 50 detects that the amount ofgenerated electricity detected by the detector 27 has become zero, thecontroller 50 determines that malfunction of the Rankine cycle apparatus20 has occurred, and controls the flow rate regulator 46. Thus, defectssuch as thermal damage to the evaporator 24 and excessive increase inthe internal pressure of the Rankine cycle apparatus 20 can be preventedeven when unexpected failure or the like has occurred in the Rankinecycle apparatus 20. When the boiler 10 is a gas boiler, defects such asthermal damage to the evaporator 24 can be prevented more reliably bystopping the supply of the fuel to the combustor 14. However, when theboiler 10 is a pellet boiler as described later, there is a possibilitythat the production of the combustion gas cannot be stopped immediately.In such a situation, defects such as thermal damage to the evaporator 24can be prevented by controlling the flow rate regulator 46 to feed alarger amount of water to the second fluid circuit 40.

When the demand for hot water is low, hot water supply from the secondfluid circuit 40 may be stopped. In this case, electricity is suppliedfrom the Rankine cycle apparatus 20, and hot water is supplied from thefirst fluid circuit 30. Since water is not fed to the second fluidcircuit 40, the thermal energy imparted to the evaporator 24 is equal tothe total of the thermal energy directly imparted from the combustiongas and the thermal energy indirectly imparted from the second heatexchanger 42 via the fins 61. That is, the evaporator 24 absorbs alarger amount of thermal energy, and the working fluid can be heated toa higher temperature. Consequently, the amount of electricity generatedby the Rankine cycle apparatus 20 is increased, and the efficiency ofelectricity generation is improved while defects such as thermal damageto the second heat exchanger 42 are prevented. The operation thus fardescribed is suitable for a situation where the demand for hot water islow and the demand for electricity is large.

<Second Operation Mode>

In the second operation mode, the Rankine cycle apparatus 20 is not inoperation, and the CHP system 100 can supply hot water alone to theoutside. The CHP system 100 is capable of heating water by feeding waterto the second heat exchanger 42 when the Rankine cycle apparatus 20 isnot generating electricity. Specifically, water is fed to the secondfluid circuit 40 so that hot water is produced by use of the secondfluid circuit 40. The second heat exchanger 42 directly absorbs heat ofthe combustion gas and, at the same time, indirectly absorbs heat of thecombustion gas via the evaporator 24. Thus, it is possible to producehot water in the second heat exchanger 42 while preventing defects suchas thermal damage to the evaporator 24 and thermal decomposition of theworking fluid, thereby improving the convenience for users. In thesecond operation mode, the flow rate regulator 46 is controlled to befully open, for example.

Hereinafter, several modifications of the CHP system will be described.The elements common between the CHP system 100 shown in FIG. 1 and eachmodification are denoted by the same reference numerals, and thedescription thereof is omitted. That is, the matters described for theCHP system 100 can apply to the modifications below unless technicalinconsistency occurs.

(First Modification)

As shown in FIG. 3, a CHP system 102 according to the first modificationincludes the first fluid circuit 30 and the second fluid circuit 40connected together in series. That is, the first fluid circuit 30 andthe second fluid circuit 40 may be connected together in series so thatthe water heated through the first fluid circuit 30 is further heatedthrough the second fluid circuit 40. In this case, higher-temperaturehot water can be produced.

Also in the present modification, the second fluid circuit 40 iscomposed of the flow path 44 a, the second heat exchanger 42, and theflow path 44 b. The flow path 44 a branches from the first fluid circuit30 at a branch point 31, and is connected to the inlet of the secondheat exchanger 42. The flow path 44 b is connected to the outlet of thesecond heat exchanger 42, and joins to the first fluid circuit 30 at ajunction point 33. In the first fluid circuit 30, the flow rateregulator 46 is disposed between the branch point 31 and the junctionpoint 33. With such a configuration, not only can all of the waterheated in the first fluid circuit 30 be further heated in the secondheat exchanger 42, but also only a portion of the water heated in thefirst fluid circuit 30 can be further heated in the second heatexchanger 42. The pressure loss of water in the second heat exchanger 42is relatively large; therefore, when the flow rate regulator 46 is fullyopened, a large portion of the water bypasses the second heat exchanger42, and only a small amount of water flows through the second heatexchanger 42. In this manner, the ratio of the amount of water bypassingthe second heat exchanger 42 to the amount of water flowing through thesecond heat exchanger 42 can be adjusted by the flow rate regulator 46.Therefore, the electrical output and the thermal output can be freelyand finely adjusted on demand. In addition, by feeding an appropriateamount of the water (for example, all of the water) to the second heatexchanger 42 when the Rankine cycle apparatus 20 is not in operation,defects such as thermal damage to the evaporator 24 and excessiveincrease in the internal pressure of the Rankine cycle apparatus 20 canbe reliably prevented. An on-off valve may be used instead of the flowrate regulator 46. This applies also to the other modifications.

(Second Modification)

As shown in FIG. 4, a CHP system 104 according to the secondmodification has, as the combustor 14, a plurality of discretecombustors 14 a, 14 b, and 14 c capable of producing flame andcombustion gas independently of each other. The positional relationshipbetween the second heat exchanger 42 and the plurality of discretecombustors 14 a, 14 b, and 14 c is determined so that the combustion gasproduced in at least one of the discrete combustors, i.e., the discretecombustor 14 a, flows without passing through the second heat exchanger42. Specifically, the second heat exchanger 42 is situated directlyabove the discrete combustors 14 b and 14 c of the plurality of discretecombustors 14 a, 14 b, and 14 c, and is not situated directly above theother discrete combustor 14 a. By contrast, the evaporator 24 issituated directly above the plurality of discrete combustors 14 a, 14 b,and 14 c. In other words, when an image of the second heat exchanger 42is orthogonally projected onto the combustor 14, the projected image ofthe second heat exchanger 42 overlaps only the discrete combustors 14 band 14 c. When an image of the evaporator 24 is orthogonally projectedonto the combustor 14, the projected image of the evaporator 24 overlapsall of the discrete combustors 14 a, 14 b, and 14 c. The combustion gasG produced in the discrete combustor 14 a travels toward the evaporator24 substantially without passing through the second heat exchanger 42.When the amount and temperature of hot water produced in the first fluidcircuit 30 are sufficient so that there is no need to additionally heatthe hot water in the second fluid circuit 40, the combustion gas G canbe delivered directly to the evaporator 24. Thus, defects such asthermal damage to the second heat exchanger 42 can be prevented.Furthermore, since the combustion gas G maintaining a high temperaturereaches the evaporator 24, the efficiency of electricity generation bythe Rankine cycle apparatus 20 can be improved.

The scales (the heating powers) of the discrete combustors 14 a, 14 b,and 14 c are not particularly limited. For example, the heating power ofthe discrete combustor 14 a may be relatively low, while the totalheating power of the discrete combustors 14 b and 14 c may be relativelyhigh. With such a configuration, the Rankine cycle apparatus 20 can beendowed with sufficient capacity to generate electricity. Conversely,the heating power of the discrete combustor 14 a may be relatively high,while the total heating power of the discrete combustors 14 b and 14 cmay be relatively low. In this case, even when the operation of theRankine cycle apparatus 20 is stopped, a sufficient amount of hot watercan be supplied. That is, sufficient space heating performance isexhibited.

The CHP system 104 further includes a third heat exchanger 48. The thirdheat exchanger 48 is disposed inside the boiler 10 so as to be locatedfarther from the combustor 14 than is the evaporator 24. The third heatexchanger 48 is, for example, a fin tube heat exchanger. The third heatexchanger 48 is not in direct contact with the evaporator 24, and a gapof appropriate width is provided between the third heat exchanger 48 andthe evaporator 24. In the present embodiment, the same heat medium asthat flowing through the second heat exchanger 42, i.e., water, flowsthrough the third heat exchanger 48. In the third heat exchanger 48, thethermal energy produced in the combustor 14 is transferred to water.With the use of the third heat exchanger 48, that remaining portion ofthe thermal energy produced in the combustor 14 which has not beenabsorbed in the evaporator 24 and the second heat exchanger 42 can berecovered. Consequently, the efficiency of use of the thermal energyproduced in the combustor 14 is improved.

In the present modification, the third heat exchanger 48 is provided inthe first fluid circuit 30 so as to further heat the water heated in thecondenser 22 of the Rankine cycle apparatus 20. To be specific, thefirst fluid circuit 30 is composed of flow paths 32 a to 32 c and thethird heat exchanger 48. The water outlet of the condenser 22 and theinlet of the third heat exchanger 48 are connected by the flow path 32b. Therefore, the water flowing in the first fluid circuit 30 is heatedin the condenser 22 by the working fluid of the Rankine cycle apparatus20, and then further heated by the residual heat of the combustion gas Gin the third heat exchanger 48. The flow path 32 c is connected to theoutlet of the third heat exchanger 48. Hot water can be supplied to theoutside through the flow path 32 c.

Additionally, in the present modification, the third heat exchanger 48is connected to the second heat exchanger 42 so that the water havingpassed through the third heat exchanger 48 flows into the second heatexchanger 42. With such a configuration, water with a relatively lowtemperature flows through the third heat exchanger 48, while water witha relatively high temperature flows through the second heat exchanger42. Therefore, a larger amount of thermal energy can be absorbed in thesecond heat exchanger 42 and the third heat exchanger 48. Consequently,the efficiency of use of the thermal energy produced in the combustor 14is improved.

More specifically, the flow path 44 a of the second fluid circuit 40branches from the flow path 32 c of the first fluid circuit 30. That is,the first fluid circuit 30 and the second fluid circuit 40 are connectedin series. In addition, the outlet of the second heat exchanger 42 andthe flow path 32 c are connected by the flow path 44 b at a junctionpoint 35 located downstream of a branch point 34 between the flow path32 c and the flow path 44 a. The hot water flowing from the second heatexchanger 42 is returned to the flow path 32 c of the first fluidcircuit 30 through the flow path 44 b. The water heated in the condenser22 is further heated in the third heat exchanger 48 and the second heatexchanger 42. Consequently, the efficiency of use of the thermal energyproduced in the combustor 14 is further improved.

In the first fluid circuit 30 (flow path 32 c), the flow rate regulator46 is disposed between the branch point 34 and the junction point 35. Bycontrol of the flow rate regulator 46, not only can all of the waterheated in the first fluid circuit 30 be further heated in the secondheat exchanger 42, but also only a portion of the water heated in thefirst fluid circuit 30 can be further heated in the second heatexchanger 42. The pressure loss of water in the second heat exchanger 42is relatively large; therefore, when the flow rate regulator 46 is fullyopened, a large portion of the water bypasses the second heat exchanger42, and only a small amount of water flows through the second heatexchanger 42. In this manner, the ratio of the amount of water bypassingthe second heat exchanger 42 to the amount of water flowing through thesecond heat exchanger 42 can be adjusted by the flow rate regulator 46.Therefore, the electrical output and the thermal output can be freelyand finely adjusted on demand. Furthermore, by feeding an appropriateamount of water to the second heat exchanger 42 when the Rankine cycleapparatus 20 is not in operation, defects such as thermal damage to theevaporator 24 and excessive increase in the internal pressure of theRankine cycle apparatus 20 can be reliably prevented.

The third heat exchanger 48 may be provided independently of the firstfluid circuit 30 and the second fluid circuit 40. In other words, thethird heat exchanger 48 may be a heat exchanger capable of heating aheat medium different from the heat medium to be heated in the firstfluid circuit 30 and the second fluid circuit 40. The third heatexchanger 48 may be provided in the CHP systems 100 and 102 previouslydescribed.

The discrete combustors 14 a, 14 b, and 14 c may each be operated alone,or two or more combustors selected from the discrete combustors 14 a, 14b, and 14 c may be operated simultaneously. For example, when theoperation of the discrete combustors 14 b and 14 c is stopped and thediscrete combustor 14 a is operated alone, substantially only theevaporator 24 receives thermal energy, and electricity and hot water areproduced by the Rankine cycle apparatus 20. When the discrete combustor14 b or 14 c is operated alone, substantially only the second heatexchanger 42 receives thermal energy, and only hot water is produced.That is, by controlling the combustor 14 on the demand for hot water andthe demand for electricity, it is possible to adjust the electricaloutput and thermal output freely, thereby improving the convenience forusers.

(Third Modification)

As shown in FIG. 5A, a CHP system 106 according to the thirdmodification includes a cylindrical combustor as the combustor 14. Flameand combustion gas are produced at the surface of the cylindricalcombustor 14. A heat exchanger (the second heat exchanger 42 in thepresent modification) is disposed around the combustor 14 so as tosurround the combustor 14. The combustion gas G flows radially, passesthrough the heat exchanger, and is discharged to the outside. Duringthis process, the water flowing in the heat exchanger receives thermalenergy from the flame and the combustion gas to become hot water.Boilers having such a structure are in widespread use mainly in Europe,and are provided, for example, by VIESSMANN in Germany.

As shown in FIG. 5B, a heat transfer tube as the second heat exchanger42 is disposed around the cylindrical combustor 14. The heat transfertube as the second heat exchanger 42 is formed in a helical shape, andsurrounds the combustor 14 at a slight distance from the combustor 14.Additionally, a heat transfer tube as the evaporator 24 is locatedfarther from the combustor 14 than is the second heat exchanger 42. Theheat transfer tube as the evaporator 24 is also formed in a helicalshape. In FIG. 5B, the second heat exchanger 42 and the evaporator 24are not in direct contact with each other. However, a portion of theheat transfer tube as the second heat exchanger 42 may be in directcontact with a portion of the heat transfer tube as the evaporator 24.In this case, heat transfer from the evaporator 24 to the second heatexchanger 42 is made possible. In the present modification, the secondheat exchanger 42 faces the cylindrical outer circumference of thecombustor 14, whereas the evaporator 24 does not face the cylindricalouter circumference of the combustor 14. A partition plate 80 isdisposed on the end face of the combustor 14. The partition plate 80extends toward the inner circumference of the second heat exchanger 42,and limits the flow path of the combustion gas G. The partition plate 80may be in contact with the second heat exchanger 42.

The combustion gas G is blown out radially outward from the combustor14, flows through the space around the second heat exchanger 42 and thespace around the evaporator 24 in this order, and then travels in theinternal space of the combustion chamber 12 toward the exhaust port. TheCHP system 106 including the combustor 14 having such a structure canalso exert the same function and provide the same effect as the CHPsystem 100 described with reference to FIG. 1. As can be seen from FIG.5B, the concept of being “in direct contact” encompasses not only thesituation where a plurality of fins is shared as in the example of FIG.2, but also the situation where the heat transfer tube constituting theevaporator 24 and the heat transfer tube constituting the second heatexchanger 42 are in line or surface contact with each other.

Also, the third heat exchanger 48 described with reference to FIG. 4 maybe provided in the CHP system 106 shown in FIG. 5A. In this case, asshown in FIG. 5C, a heat transfer tube as the third heat exchanger 48 isdisposed inside the combustion chamber 12 so as to be located fartherfrom the combustor 14 than is the evaporator 24. The heat transfer tubeas the third heat exchanger 48 is also formed in a helical shape. Apartition plate 81 is additionally provided so as to partially separatethe space around the evaporator 24 from the space around the third heatexchanger 48. A partition plate 82 is additionally provided so that thecombustion gas G flows radially outward from the vicinity of the centerof the helically-shaped third heat exchanger 48. The combustion gas G isblown out radially outward from the combustor 14, and flows through thespace around the second heat exchanger 42, the space around theevaporator 24, and the space around the third heat exchanger 48 in thisorder. The water heated in the third heat exchanger 48 can be furtherheated in the second heat exchanger 42.

Also in the CHP system 106 of the present modification, the first fluidcircuit 30 is, as shown in FIG. 5A, connected to the second fluidcircuit 40 in series as in the CHP system 102 of the first modification.Also in the present modification, by control of the flow rate regulator46, not only can all of the water heated in the first fluid circuit 30be further heated in the second heat exchanger 42, but also only aportion of the water heated in the first fluid circuit 30 can be furtherheated in the second heat exchanger 42. Therefore, higher-temperaturehot water can be produced as in the CHP system 102 of the firstmodification. The electrical output and the thermal output can be freelyand finely adjusted on demand. Furthermore, by feeding an appropriateamount of water to the second heat exchanger 42 when the Rankine cycleapparatus 20 is not in operation, defects such as thermal damage to theevaporator 24 and excessive increase in the internal pressure of theRankine cycle apparatus 20 can be reliably prevented.

(Fourth Modification)

As shown in FIG. 6, a CHP system 108 according to the fourthmodification includes, as the boiler 10, a pellet boiler instead of agas boiler. When the boiler 10 is a pellet boiler, the combustor 14produces high-temperature combustion gas by combusting a solid fuel,such as wood pellet, coal, and biomass, in the pellet boiler.

In the present modification, the boiler 10 includes a flue(s) 15disposed directly above the combustor 14. The flue is a path of thecombustion gas G, and extends from the combustor 14 toward the exhaustport. The second heat exchanger 42, the evaporator 24, and the thirdheat exchanger 48 are arranged in order of increasing distance from thecombustor 14. The second heat exchanger 42, the evaporator 24, and thethird heat exchanger 48 can each be constituted by a heat transfer tubewound around the flue 15. The heat transfer tube as the second heatexchanger 42 is in direct contact with the heat transfer tube as theevaporator 24. Therefore, the CHP system 108 according to the presentmodification can also exert the same function and provide the sameeffect as the CHP system 100 described with reference to FIG. 1.

Also in the CHP system 108 of the present modification, the first fluidcircuit 30 is connected to the second fluid circuit 40 in series as inthe CHP system 104 of the second modification or the CHP system 106 ofthe third modification. The configurations of the first fluid circuit 30and the second fluid circuit 40 in the present modification are the sameas those of the first fluid circuit 30 and the second fluid circuit 40in the second modification or the third modification. Therefore, alsofor the first fluid circuit 30 and the second fluid circuit 40 in thepresent modification, the same effects as those in the secondmodification and the third modification can be obtained

(Fifth Modification)

As shown in FIG. 7, a CHP system 110 according to the fifth modificationalso includes a pellet boiler as the boiler 10. The difference betweenthe present modification and the fourth modification lies in thepositional relationship among the flue 15, the evaporator 24, and thesecond heat exchanger 42. In the present modification, the second heatexchanger 42 is located relatively close to the flue 15, and theevaporator 24 is located relatively far from the flue 15. A heattransfer tube as the second heat exchanger 42 is disposed around theflue 15. Specifically, the heat transfer tube as the second heatexchanger 42 is wound on the flue 15. A heat transfer tube as theevaporator 24 is disposed outwardly of the second heat exchanger 42 inthe radial direction of the flue 15. Specifically, the heat transfertube as the evaporator 24 is wound on the second heat exchanger 42. Theheat transfer tube as the second heat exchanger 42 and the heat transfertube as the evaporator 24 are in contact with each other in the radialdirection of the flue 15. The heat transfer tube as the second heatexchanger 42 and the heat transfer tube as the evaporator 24 each have ahelical shape and extend vertically along the flue 15. A pair of theevaporator 24 and the second heat exchanger 42 is disposed around eachof the plurality of flues 15. In order that the flow direction of thecombustion gas G in the flue 15 and the flow direction of the heatmedium in the second heat exchanger 42 may be opposite to each other,the inlet of the second heat exchanger 42 is formed so as to be locatedrelatively far from the combustor 14 (on the downstream side of the flue15), and the outlet of the second heat exchanger 42 is formed so as tobe located relatively close to the combustor 14 (on the upstream side ofthe flue 15). Thus, efficient heat exchange takes place between thecombustion gas G flowing in the flue 15 and the heating medium flowingin the second heat exchanger 42. This applies also to the evaporator 24.

When the boiler 10 is a pellet boiler, not only the distance from thecombustor 14 but also the distance from the flue 15 acts as a factorinfluencing the amount of heat input to the evaporator 24 and the secondheat exchanger 42. Assuming the flue 15 as a heat source, the secondheat exchanger 42 is located closer to the heat source than is theevaporator 24. Also in the present modification, the same effects asthose of the CHP systems 100 to 108 previously described can beobtained.

(Other Modifications)

It is not essential that the evaporator 24 be in direct contact with thesecond heat exchanger 42. The evaporator 24 may be spaced apart from thesecond heat exchanger 42. For example, a gap as formed between theevaporator 24 and the third heat exchanger 48 may be provided betweenthe evaporator 24 and the second heat exchanger 42. Even when theevaporator 24 is in contact with the second heat exchanger 42, it is notessential that the contact of the evaporator 24 with the second heatexchanger 42 be directly made. The evaporator 24 may be in indirectcontact with the second heat exchanger 42 via a thermally-conductivemember. The thermally-conductive member is a member that makes thermalconnection between the evaporator 24 and the second heat exchanger 42.An example of the thermally-conductive member is a heat pipe.

A heat exchange unit 70 shown in FIG. 8A is formed of the evaporator 24,the second heat exchanger 42, and a heat pipe 54. In the heat exchangeunit 70, the evaporator 24 is not in direct contact with the second heatexchanger 42. The evaporator 24 is disposed directly above the secondheat exchanger 42. The evaporator 24 and the second heat exchanger 42face each other. A gap of certain width is provided between theevaporator 24 and the second heat exchanger 42. The heat pipe 54 thatallows the evaporator 24 and the second heat exchanger 42 to be inindirect contact with each other is provided so that heat of theevaporator 24 is sufficiently transferred to the second heat exchanger42. Such a heat pipe 54 is often used to facilitate heat transfer fromone object to another. The heat pipe 54 can be composed of a pipe madeof a material having high thermal conductivity and a volatile mediumenclosed inside the pipe. By heating one end of the pipe and cooling theother end, the cycle of evaporation and condensation of the volatilemedium is made to occur in the pipe. As a result, heat transfers fromthe one end to the other end of the pipe.

As shown in FIG. 8B, the heat pipe 54 has a heat absorption portion 54 aand a heat release portion 54 b. The heat absorption portion 54 a andthe heat release portion 54 b are in direct contact with the evaporator24 and the second heat exchanger 42, respectively. Specifically, theheat absorption portion 54 a pierces through the fins of the evaporator24, and thus the heat absorption portion 54 a is fixed to the evaporator24. The heat release portion 54 b pierces through the fins of the secondheat exchanger 42, and thus the heat release portion 54 b is fixed tothe second heat exchanger 42. With such a configuration, the heattransfer from the evaporator 24 to the second heat exchanger 42 can befacilitated.

Obviously, the heat pipe 54 can be used also when, as in a heat exchangeunit 72 shown in FIG. 8C, the evaporator 24 is in direct contact withthe second heat exchanger 42.

INDUSTRIAL APPLICABILITY

The CHP systems disclosed in the present description can heat a heatmedium such as water even when the Rankine cycle apparatus is not inoperation. Such CHP systems are particularly suitable for use in coldregions in which it is customary to produce hot water for indoor heatingby a boiler. That is, the techniques disclosed in the presentdescription can enhance the capacity of CHP systems to supply hot water,and also make it possible to continue indoor heating even when theRankine cycle apparatus gets out of order for some reason.

The present invention may be embodied in other forms without departingfrom the spirit or essential characteristics thereof. The embodimentsdisclosed in this specification are to be considered in all respects asillustrative and not limiting. The scope of the present invention isindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are intended to be embraced therein.

What is claimed is:
 1. A combined heat and power system comprising: aheat source; a Rankine cycle apparatus comprising, as an evaporator forheating a working fluid, a first heat exchanger that absorbs thermalenergy produced in the heat source; a second heat exchanger that is aheat exchanger for heating a heat medium different from the workingfluid of the Rankine cycle apparatus, that is located closer to the heatsource than is the first heat exchanger, and that absorbs thermal energyproduced in the heat source and transfers the thermal energy to the heatmedium; and a fluid circuit that includes the second heat exchanger,wherein the working fluid is an organic working fluid, the heat mediumis in a single-phase state selected from a gas-phase state and aliquid-phase state in the second heat exchanger, no heat exchanger usedto heat the working fluid is provided upstream of the second heatexchanger in a flow path of a medium that imparts the thermal energy tothe working fluid and the heat medium, and the fluid circuit is notfluidly connected with the flow path of the medium that imparts thethermal energy to the working fluid and the heat medium.
 2. The combinedheat and power system according to claim 1, wherein the second heatexchanger is in direct contact with the first heat exchanger or inindirect contact with the first heat exchanger via athermally-conductive member.
 3. The combined heat and power systemaccording to claim 1, wherein the heat source is a combustor thatproduces flame and combustion gas that serves as the medium.
 4. Thecombined heat and power system according to claim 3, wherein the firstheat exchanger and the second heat exchanger are disposed on the flowpath of the combustion gas so that the combustion gas passes through thesecond heat exchanger and the first heat exchanger in this order.
 5. Thecombined heat and power system according to claim 1, further comprising:a flow rate regulator, wherein the fluid circuit includes a flow paththat feeds the heat medium to the second heat exchanger, and the flowrate regulator is disposed in the flow path.
 6. The combined heat andpower system according to claim 5, wherein the Rankine cycle apparatuscomprises a detector that detects an amount of generated electricity,and the combined heat and power system further comprises a controllerthat controls the flow rate regulator based on the amount of generatedelectricity detected by the detector.
 7. The combined heat and powersystem according to claim 1, wherein the combined heat and power systemis capable of heating the heat medium by feeding the heat medium to thesecond heat exchanger when the Rankine cycle apparatus is not generatingelectricity.
 8. The combined heat and power system according to claim 3,wherein the combustor comprises a plurality of discrete combustorscapable of producing the flame and the combustion gas independently ofeach other, and a positional relationship between the second heatexchanger and the plurality of discrete combustors is determined so thatthe combustion gas produced in at least one of the discrete combustorsflows without passing through the second heat exchanger.
 9. The combinedheat and power system according to claim 1, further comprising a thirdheat exchanger located farther from the heat source than is the firstheat exchanger, wherein the third heat exchanger transfers thermalenergy produced in the heat source to the heat medium.
 10. The combinedheat and power system according to claim 9, wherein the third heatexchanger is connected to the second heat exchanger so that the heatmedium having passed through the third heat exchanger flows into thesecond heat exchanger.
 11. The combined heat and power system accordingto claim 2, wherein the thermally-conductive member is a heat pipe thatallows the first heat exchanger and the second heat exchanger to be inindirect contact with each other.
 12. The combined heat and power systemaccording to claim 1, wherein the Rankine cycle apparatus is configuredso that the working fluid receives the thermal energy only from a singlemedium.
 13. The combined heat and power system according to claim 1,wherein the heat medium is water, and the fluid circuit is a circuit forproducing hot water and supplying the hot water to the outside of thecombined heat and power system.
 14. The combined heat and power systemaccording to claim 13, wherein the combined heat and power system iscapable of supplying electricity alone to the outside of the combinedheat and power system while stopping supply of the hot water.
 15. Thecombined heat and power system according to claim 1, wherein a phasestate of the medium that imparts the thermal energy to the working fluidand the heat medium is different from a phase state of the heat mediumin the fluid circuit.
 16. The combined heat and power system accordingto claim 1, wherein a phase state of the medium is a gas phase and aphase state of the heat medium is a liquid phase.